If you are working on a large project, you inevitably end up with a large edmx file if you are doing database first EF work. One tip I like to follow is to export it to a pd file so that I can look at it as a referrence while developing. To do this you firstly need to have a print driver installed that will create PDF files. A good one to chose is PDF Creator from pdfforge, however do a virus scan on this file as my AVG came up with a warning about AdLoad.OpenCandy adware program included in the installation. Once PDF Creator is installed, open up your EDMX file in Visual Studio and go to File > Print Chose PDFCreator as the printer and click the Properties button
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Keep it as Portrait if you wish, then press the Advanced button
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  Choose ARCH E3 as the Paper Size. This is an architectural size and measures 27 x 39 inches (686 mm× 991 mm)  
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  Come back out by clicking the OK buttons until you get to print the document. In the PDF Creator options screen, set the profile to High Quality; it will create a larger file, but will be much clearer when zooming in.  
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The simply save it. Happy codeing